Showing papers by "Stephen Bell published in 2009"
TL;DR: In this article, two conformers have been identified with one the cis form where the methyl group is over the three-membered ring and the other the gauche form with gauche the more stable conformer.
11 citations
TL;DR: In this paper, the authors used ab initio MP2 (full) and DFT (B3LYP method) calculations to identify stable conformers of 2,2-difluoroethanol.
Abstract: The infrared spectra (4,000–30 cm−1) of the gas and solid and the Raman spectrum of liquid 2,2-difluoroethanol as well as variable temperature infrared spectra of krypton/xenon solutions have been recorded. From all these data, two (Gg and Tg) out of the five possible stable conformers have been confidently identified. The order of the stabilities has been predicted to be Gg > Tg > Gt > Gg′ > Tt by utilizing ab initio MP2 (full) and DFT (B3LYP method) calculations, where the first indicator (capital letter) is in reference to rotation around the C–C bond (G = gauche or T = trans) and the second one (small letter) refers to the orientation of the hydroxyl group. The percentage of the minor conformer Tg, at ambient temperature, is estimated to be (16 ± 3%). The optimized geometries, fundamental frequencies, infrared intensities, Raman activities, and depolarization values as well as centrifugal distortion constants have been obtained from ab initio and density functional theory calculations by utilizing a variety of basis sets as well as those with diffuse functions. By utilizing the previously reported microwave rotational constants for two isotopomers of the Gg conformer combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r
0 parameters have been obtained. The determined heavy atom distances (A) for the Gg conformer are: C1–C2 = 1.510(3), C2–F4 = 1.371(3), C2–F5 = 1.362(3), C1–O3 = 1.412(3) A and angles ∠O3C1C2 = 111.0(5), ∠F4C2C1 = 108.8(5), ∠F5C2C1 = 109.8(5), τF4C2C1O3 = 63.5(5), τF5C2C1O3 = 179.1(5)°. Barriers of internal rotation have been obtained and vibrational assignments for the Gg and Tg conformers are given. The five predicted centrifugal distortion constants compared to the experimental values are in reasonable agreement except for ∆K, which appears to be in error. The results are discussed and the structural parameters compared to the corresponding ones for 2-fluoroethanol and 2,2,2-trifluoroethanol where those for the latter molecule have been redetermined. The currently determined heavy atom parameters are quite different from the earlier assumed values, which led to poor values of the six adjusted parameters.
9 citations